estimate time for compilation on each platform

Give the developer the estimated time it takes to compile Pd on each platform.

For Windows:

1. install msys - 5 minutes Note: unclick the box that says "run when finished"
2. from start menu, run mingw-64 win32 environment - less than a minute
3. pacman packages - 5 minutes
4. exit - less than a minute
5. download repo - 3 minutes
6. git submodule init and git submodule sync and git submodule update for gem - 3 minutes
7. download and place nw.js binary in pure-data/nw/nw - 5 minutes
8. download asio - less than a minute
9. copy asio - less than a minute
10. remove "flext" from externals/Makefile - 1 minute
11. download nw.js binary, name it "nw", and copy it to purr-data/pd/nw - 3 minutes
12. make install - 45 minutes

fix issue with flext